STEAM TURBINES

Where the blade stresses are too high for convenient use of phosphor
bronze, steel blades are adopted, milled out of the solid bar. The blade
roots are either dovetailed (fig. 30) and fit into corresponding slots in the

Fig. 31.—Moving Blades
with Inverted Dovetails,
for Curtis Turbines.

rim of the disc, or where the disc
stresses are such as to make it
preferable to reduce the rim
thickness to a minimum, then the
blade roots are milled with an in-
verted dovetail as shown in fig. 31.
Fig. 32 shows a section of
guide blades to reverse the direc-
tion of motion of the steam be-
tween velocity stages. These blades are made in a similar manner to the run-
ning blades, and are fitted into a cast-iron ring which is bolted to the casing
or the nozzle plate. The arc covered by the guide blades is practically equal
to that covered by the first stage nozzles, so that where the nozzles are con-
fined to the top half of the casing the same applies to the guide-blade ring.
. The British Thomson-Houston Company adopt flexible claw-type coup-